Although applicable to other types of vehicles, the invention will be described in connection with railroad or railway vehicles, such as railway cars, locomotives, etc.
Railway vehicles usually have brake shoes engageable with the vehicle wheels. Such shoes are forced against the wheels by an air operable piston and cylinder assembly acting through a brake rigging mounted on the vehicle and connected to the shoes. Such brake shoe operation is used to slow the vehicle down or to bring the vehicle to a halt.
However, when the vehicle is to be parked for any significant period of time, such as in a terminal, freight yard, etc., the system described hereinbefore is not used, and instead, the vehicle is prevented from moving by applying braking force to the shoes by driving apparatus which can be operated manually and locked in the status which continuously applies the braking force. Usually, the driving apparatus is connected to the brake shoes through at least a portion of the brake rigging mentioned hereinbefore. See, for example, U.S. Pat. Nos. 829,032; 3,176,539 and 4,291,793.
Parking brake drives which can be actuated either manually or by the energization of an electric motor have been proposed. See, for example, U.S. Pat. Nos. 829,032; 1,491,753; 6,039,158 and 6,427,811.
Typically, a parking brake drive comprises a stamped or cast hand wheel, a stamped or cast steel housing enclosing at least two steel gears and a chain which attaches to the vehicle brake rigging and to a chain gear in the housing. See, for example, U.S. Pat. No. 3,176,539. The parking brake is applied by rotating the hand wheel in a clockwise direction which causes a gear train inside the housing to rotate. The last gear in the system is attached to one end of the chain by either a pin or a pocketed drum, which fits the chain. As the hand wheel is rotated and the gear train rotates, the chain is wound onto the drum causing the vehicle brake system to apply braking force to wheels of the vehicle.
Typically, the rail industry standard is that the application of 125 pounds of force to the rim of the hand wheel will set the parking brake. The requirement of being able to apply 125 pounds to the hand wheel is quite demanding. A weaker person cannot readily release the hand brake if a stronger person has applied it. The parking brake can be set with more uniformity using an electrically operable gear motor to drive the gear train. This allows the parking brake to be set without the possibility of injury to the operator.
In addition, it is desirable to be able to set and release the brakes coupled to the brake drive by either operation of the motor drive or of the manual drive.
The hand brake drive described in U.S. Pat. No. 6,427,811 requires an electrically operable clutch for the electrical motor drive and a ratchet wheel and pawl coupling of the manually operable handle which depends upon the position of the handle. The drive also requires a second ratchet wheel and pawl operable by a solenoid to hold the brakes in their “set” positions and to release the brakes whether the brakes are “set” by the motor drive or manually. Therefore, the drive requires two ratchet wheel and pawl mechanisms and two electrically operable, physically movable components in the housing which is subject to the accumulation of dust, grease, etc. In addition, if the manual handle does not happen to be in a vertical position, or its ratchet wheel and pawl connection is defective, the handle will move when the brakes are released and slam against the housing and not only create a hazard to operating personnel but also prevent release of the brakes.
The hand brake drive described in U.S. Pat. No. 6,039,158 also requires an electrically operable clutch which slips when the brakes are set, and two ratchet wheel and pawl mechanisms in the housing, one of which, the ratchet handle mechanism, is dependent on the handle position and the other of which can be released only manually. Thus, the drive is not entirely satisfactory for reasons that the drive of U.S. Pat. No. 6,427,811 is not entirely satisfactory. In addition, the brakes can be released only by manually pulling a release handle at the housing whether the brakes are set manually or by the motor drive.
It is not desirable that the manual drive, e.g. the hand wheel or handle move when the brakes are released to avoid injury to train crew and that the brakes be settable and releasable either by the motor drive or the manual drive. It is also desirable to have an indicator which indicates the status of the brakes and which can be located remotely from the parking brake drive, e.g. if the parking brake drive is on a locomotive at a portion remote from the engineer's cab, it is convenient and/or desirable to locate the indicator and the motor drive control in the cab.